The present invention relates to the field of additives for fluids such as automatic transmission fluids, traction fluids, fluids for continuously variable transmission fluids (CVTs), dual clutch automatic transmission fluids, farm tractor fluids, and engine lubricants.
In the automatic transmission marketplace, where there is rapid engineering change driven by the desire to reduce weight and increase transmission capacity, there is a desire for automatic transmission fluids that exhibit a high static coefficient of friction for improved clutch holding capacity. At the same time, there is a desire to improve the retention of positive slope characteristics in the mu/v (coefficient of friction vs. sliding speed) curve. There are newer tests in the marketplace which are used to define these characteristics. The static torque can be measured in tests such as the Toyota SAE#2 friction test procedure and the retention of positive slope can be measured by procedures like the JASO LVFA (Japan Automotive Standards Organization, Low Velocity Friction Apparatus) in which the slope of the mu/v curve is periodically measured during oxidative and mechanical aging.
There are patents, for example, U.S. Pat. No. 5,750,476, where a type of friction modifier technology used to achieve this performance is described. The combined requirements of high static coefficient of friction and durable positive slope are often incompatible with traditional ATF friction modifier technology which is extremely well described in the patent literature. Many of the commonly used friction modifiers result in a low static coefficient of friction and are not durable enough on positive slope to be of sufficient use. Additional patent literature describing technology for retaining positive mu/v or anti-shudder characteristics include U.S. Pat. No. 5,858,929. These may employ metal detergents and combinations of friction modifiers.
U.S. Pat. No. 4,886,612 discloses a lubricating oil comprising at least one of various products, which can be various imidazolines or an oxazoline of the structure
where R2 and R3 each represent CH2OCOR1, CH2OH or H.
The present invention, therefore, solves the problem of developing new friction modifiers to obtain high static coefficients of friction and maintaining a durable positive slope during oxidative and mechanical stressing of the friction system, particularly in an automatic transmission by the use of a friction modifier prepared by the condensation a carboxylic acid (or a reactive equivalent thereof) with an amino alcohol; for example, the condensation of two moles of isostearic acid with one mole of tris-hydroxymethylaminomethane (THAM).